This invention deals generally with fences and more particularly with a fixture for mounting a hollow fence post on a vertical pipe.
Plastic or vinyl fences have become quite common. They are particularly desirable because they are light weight, strong, attractive, and virtually maintenance free. Since the color of such fences is an integral part of the material they need no painting either initially or later in use, and their greatest asset may be the inherent weather resistance of the materials. A plastic structure such as a fence post can be expected to last indefinitely, even in the most severe environment, with no sign of deterioration.
However, to attain the low cost available from such materials as vinyl or other plastics, most fence posts are manufactured as hollow structures, and some sort of fitting is required to attach them to a horizontal base structures such as the earth, concrete pads, or wooden decks. There have been several patents issued on various devices to accomplish the installation of hollow vertical plastic fence posts to such horizontal base structures.
U.S. Pat. No. 5,359,827 to Gehman discloses an open vertical frame structure with a rectangular bottom plate attached to a base structure and angle irons attached to the bottom plate at its corners. A nut atop a threaded central rod is used to force a dished top plate down between the angle irons and force them outward into locking contact with the interior surfaces of a hollow post, thus locking the post in place.
U.S. Pat. No. 5,704,188 to Coulis uses coiled springs which fit tightly around an anchored pipe, with the coiled springs having extensions that fit tightly into the corners of a hollow rectangular post.
U.S. Pat. No. 5,755,431 to Williams discloses a fixture which holds a hollow rectangular post on a stake that has a xe2x80x9cTxe2x80x9d shaped cross section. The fixture has a generally triangular shape, with outer surfaces extending perpendicularly to an inner web and a central structure constructed to fit over the xe2x80x9cTxe2x80x9d shape of the stake that is driven into the ground.
Such prior art structures are not only very complex and expensive to fabricate, but also have limited versatility. It would be very desirable to have an easily manufactured, simple device to attach hollow vertical square posts to different base structures.
The present invention is a mounting fixture to attach a square plastic fence post to a simple pipe, perhaps the most widely used support structure for such fence posts. Pipe is a desirable support structure because it can be cut to any desired length, and it can easily be attached to all of the base surfaces in general use. For a simple earth base, a pipe needs only to be driven into the ground. For a wooden deck, a pipe can be attached by mounting a conventional pipe flange on the surface with screws and threading the pipe into the flange, and for a concrete base, the pipe can be anchored with new concrete set into a hole cut into the concrete base.
The fixture of the preferred embodiment of the invention is basically constructed as two concentric cylinders that are slightly offset longitudinally. The inner cylinder is sized to fit snugly over the pipe which is to be the support for the fence post, and the outer cylinder is dimensioned so that the inner surfaces of the hollow fence post fit tightly over its outer surface.
The two cylinders are attached and spaced apart by at least four fins projecting between them and by a solid surface that spans the space between them at the location of the upper end of the outer cylinder. The use of four spacing fins significantly strengthens the structure over the geometric minimum number of three. It also reduces the circumferential spacing between the fins to accommodate to the four pressure points between the outer surface of the outer cylinder and the inner surface of the square cross section of the fence post held on the outside of the outer cylinder.
The fixture""s cylinders are offset along their common axis so that the inner cylinder extends beyond the outer cylinder for access to mounting holes in the inner cylinder for inserting screws to lock the fixture onto the pipe to which it is to be attached.
Other subtle but vital features make the fixture stronger and easier to use. There are small ridges along the inner surface of the inner cylinder to contact the support pipe and prevent irregularities in the pipe from stopping the fixture as it slides along the pipe. Another feature is the addition of thicker sections of the inner cylinder through which the mounting holes penetrate. These thicker sections strengthen the inner cylinder at points where there is particularly high stress. Without the additional strength from the added thickness, the inner cylinder has a tendency to crack when the holding screws are tightened. Another feature is a slight inward taper along the upper portion of the outer surface of the outer cylinder. This taper furnishes the advantage of being able to slide the fence post over the mounting fixture without first exactly centering it.
The mounting fixture of the preferred embodiment thereby furnishes a reliable means for attaching a hollow square fence post to a simple pipe, and the fixture is easily injection molded using a minimum of material.